Storage devices such as optical disks and systems are required to function reliably over fairly wide temperature ranges. For example, the Philips-Sony Orange Book, Part II specifications pertaining to writable compact disk (CDR), specifies an operational range of -5 Celsius to +55 Celsius. The laser marking process is fundamentally a thermally driven phenomenon. It can, however, be augmented by other means; for example, applied magnetic fields, for Magneto-optic (MO) recording. In actual operation, the internal temperature of the recording device (drive) is often many tens of degrees Celsius above the ambient temperature. Therefore, there is a distinct possibility that at the moment of insertion of a CDR into a drive, an appreciable differential could exist between the CDR temperature and the internal drive temperature. Of course, over a period of time, the CDR temperature would equilibrate to the mean temperature within the drive. Many important procedures such as power calibration are undertaken immediately following CDR insertion when the media temperature may be closer to the external ambient temperature than to the internal drive temperature. Since this calibration is essentially a thermally based process it is very sensitive to the initial temperature of the CDR. Subsequent writing, undertaken when the disc has reached the internal temperature of the drive, is likely to be sub-optimal due to the possibility of over-powered recording conditions.
Thermocouple-based temperature sensing is perhaps the dominant, cost effective method currently used for temperature sensing applications. However, it requires a hard link to be established between the probe and measurement assemblies. Infra-red sensitive devices permit remote temperature sensing but are quite expensive and are sensitive to turbulence or thermal fluctuations in the intervening environment.